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Ultrasound acquisition and analysis. Comparison of current methods [abstract]

G. Pavan and M. Manghi (1997). Ultrasound acquisition and analysis. Comparison of current methods [abstract]. Bioacoustics, Volume 8 (3-4): 277 -278



Instrumentation recorders designed to record ultrasounds are very expensive and not well suited for field use; thus, cheaper devices to detect and possibly record ultrasound were developed for field research, mainly to study echolocation in bats. These are called bat detectors. Basically they employ three methods for making ultrasounds more manageable: heterodyne conversion, frequency count-down, and time-expansion. Only the last method enables the complete recording of all the features of the ultrasonic signals. It is based on digital recording with a high enough sampling rate (typically ranging between 300 and 400 ksamples/sec) and on the subsequent playback at a reduced sample rate to lower ultrasonic frequencies to within the range of conventional audio recorders. This procedure does not allow long recordings. Better suited to long recordings is digital acquisition on a PC, and several acquisition boards on the market allow for this. We developed a Pc-based Digital Signal Processing Workstation (DSPW), based on a Microstar DAP 2400E/6 acquisition board, to allow recording and playback of acoustic signals up to 150 kHz with a resolution of 12 bits (72 (IB dynamic range). The actually available Pentium CPUS allow, together with highly optimized custom-made software, analysis and display of spectrograms in real-time up to 150 kHz while performing hard-disk recording and other data analysis and logging tasks. A sharp anti-aliasing filter is required to prevent aliasing. When sampling at 312.5 ks/sec a 2 GB hard disk allows the continuous recording of up to 56 minutes. This instrumentation is very useful in laboratory experiments to monitor the ultrasonic activities of the research subjects and to optimize the instrumental setup (minimization of noise sources, microphone placement). Also it allows immediate evaluation of the results of an experiment instead of waiting for later analyses on the recordings. Special analysis procedures enable data to be logged in real-time (onset, offset, freq. tracking) and reports about the monitored signals to be produced.